The invention relates to a cylinder head gasket with a gasket plate comprising a plurality of sheet metal layers and at least one combustion chamber opening and defining a gasket plane, an inner layer being arranged in the gasket plate directly between two functional layers having sealing beads arranged one over the other, which enclose the combustion chamber opening and have bead feet lying in the planes of the functional layers and bead crests with which the sealing beads of the two functional layers all project over the functional layers in a first direction extending perpendicularly to the gasket plane, at least one ring zone of the inner layer lying between the sealing beads being clamped between the bead feet of the one functional layer and at least one bead crest of the other functional layer when the gasket is installed.
Metal layers of a flat gasket consisting of a spring steel and having beads deformable in a resilient manner in their height for sealing around an opening to be sealed are referred to in technical terminology as functional layers.
Such a cylinder head gasket may also have a third functional layer arranged outside the set of layers formed by the two other functional layers and the inner layer.
Cylinder head gaskets of the kind defined hereinabove with a plurality of functional layers are suited, above all, for engines with a larger range of sealing gap dynamics (change over time in the width or breadth of the gap between the opposed sealing surfaces of a cylinder head and an engine block during operation of the engine). In these cylinder head gaskets, a beadless inner layer (usually called carrier sheet) is used to achieve a desired compression of the engine (compression in the cylinders) by a corresponding installation thickness of the cylinder head gasket (the installation thickness denotes the thickness of the gasket in the installed state when the engine is at a standstill).
Since in cylinder head gaskets of the kind defined at the outset, in which the sealing beads of the functional layers have, in accordance with standard practice, an approximately circular arc-shaped cross section, i.e., are formed as so-called full beads, a ring zone, surrounding a combustion chamber opening, of the carrier sheet, i.e., of the inner layer, lies between the convex side of a sealing bead of the one functional layer and the concave side of a sealing bead of the other functional layer, the crest of the sealing bead of the one functional layer is pressed, when the cylinder head gasket is installed, approximately in the shape of a line, i.e., with a large specific surface pressure (pressing force in relation to the contact surface) against the aforementioned ring zone of the carrier sheet, which causes an arching of the carrier sheet along this ring zone, as the carrier sheet above the crest of the sealing bead of the one functional layer is not supported by the other functional layer, but rather is able to enter the concave region of the sealing bead of the other functional layer. The spring-back potential of the sealing bead of the one functional layer is reduced by this deformation of the carrier sheet as pressing against the carrier sheet with a specific surface pressure that is required for a reliable sealing effect can no longer be brought about by the sealing bead on account of the arching of the carrier sheet when the width or breadth of the sealing gap between cylinder head and engine block increases over time during operation of the engine. The known cylinder head gaskets of the kind defined at the outset, therefore, have the disadvantage of allowing a smaller range of sealing gap dynamics if sealing against issue of combustion gases is to be reliably effected around a combustion chamber opening.